Not All Furnaces Are the Same — What You Need to Know Before Winter
- D1 Home Inspections
- May 11
- 2 min read
When the weather cools down in Oklahoma, your furnace becomes one of the most important systems in your home. But did you know not all furnaces are the same? In this post, we’ll break down the key differences between common furnace types, why inspections matter, and what we look for when we inspect your heating system.
The Two Most Common Furnace Types
Category I Furnaces
Mid-efficiency (~80% AFUE)
Vented through the roof using metal flue (Type B vent)
Relies on gravity and indoor air to vent combustion gases
No condensate production
Category IV Furnaces
High efficiency (90%+ AFUE)
Sealed combustion with direct sidewall or rooftop PVC venting
Requires a condensate drain
More energy-efficient but more sensitive to installation issues
Understanding these differences is important because each system has its own inspection points—and potential failure risks.
Why Furnace Inspections Matter
A furnace might heat your home just fine... but still have hidden safety or efficiency issues. Here’s what a D1 Home Inspection can uncover:
Improperly sloped or terminated venting (CO hazard)
Rusted burners or blocked combustion air
Drain line leaks on high-efficiency units
Oversized or missing filters
Advanced wear and tear (often missed in newer homes)
These issues can impact your comfort, energy bills, and safety. That’s why we take the time to inspect every accessible part of your furnace.
What We Check During a Furnace Inspection
Our Oklahoma-standard furnace inspection includes:
Identifying system type and energy source
Checking visible signs of corrosion or rust
Observing flame pattern and burner condition (if accessible)
Inspecting exhaust venting for material, slope, and termination
Noting filter size, type, and condition
Documenting system age if serial number is visible
Confirming presence and visibility of shutoff valves
We inspect what’s visible and accessible—and always note what isn’t.
Additional Resources for Homeowners
Want to learn more about your furnace system and how to maintain it?
Energy.gov – Heating Systems Overview
InterNACHI Gas Furnace Inspection Checklist 2.pdf
Final Thoughts
Whether your furnace is brand new or nearing retirement, it pays to have a trained eye on it—especially before winter hits. At D1 Home Inspections, we treat every furnace inspection as an opportunity to protect your comfort and your wallet.
Have questions about your home’s heating system? Contact D1 today or ask about this during your next inspection—we’re here to help.
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